Joint mounted on rolling bearings

ABSTRACT

A joint with a pin ( 1 ) comprising an inner member ( 2 ), a center member ( 6 ), a housing body ( 8 ) and a flange ring ( 12 ) arranged in one another via rolling bearings ( 4,5,10,13,14,18,19,20 ) for pivoting or rotating about their rotational axis ( 3,7,15 ) which advantageously create a rolling bearing-mounted joint which has a high rigidity and a comparatively low frictional and pivoting resistance useful for achieving a high positioning precision in machine tools of a hexapod system.

FIELD OF THE INVENTION

The invention concerns a joint having a pin which carries an elementthat is received via a rolling bearing for pivoting in an associatedhousing.

BACKGROUND OF THE INVENTION

If the element that receives the pin is spherical in shape and pivotablein a socket, these joints are called ball-and-socket joints. Such arolling bearing-mounted ball-and-socket joint is known from U.S. Pat.No. 2,971,770. The pin is rotatably secured by a ball bearing to theflat undersurface of the spherical element which is mounted with itssemispherical surface through a plurality of small bearing balls forpivoting in a spherical recess. Ball-and-socket joints of this type areused in the field of front wheel suspensions of automotive vehicles. Thedrawback of these rolling bearing-mounted ball-and-socket joints is, onthe one hand, that due to the pointwise contact of the spherical elementwith a plurality of small bearing balls, high Hertzian stresses occurand, on the other hand, these joints possess an inadequate rigidity.

However, in addition to the automotive industry, other uses are alsoconceivable in which a low rigidity of the joints is undesirable. Thisis the case in the sector of machine tools when omnidirectionallyorientable joints are used for the positioning of tools. In this case,joints are required that can effect a pin-point positioning of a tool.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to create a rollingbearing-mounted joint which avoids the drawbacks of prior artball-and-socket joints while at least attaining their angles of pivot.

The invention achieves this object by a pin (1) that is received by aninner member (2), this inner member (2) is received via rolling bearings(4,5,19,20) arranged on its outer peripheral surface for pivoting aboutits rotational axis (3) in a center member (6), this center member (6)is received offset at 90° to the rotational axis (3) of the inner member(2) via rolling bearings (9,10) arranged on its outer peripheral surfacefor pivoting about its rotational axis (7) in a housing body (8), andthe housing body (8) is mounted offset at 900 to the rotational axis (3)of the inner member 92) and to the rotational axis (7) of the centermember (6) in a flange ring (12) via rolling bearings (13,14,18)arranged on its outer peripheral surface for rotation about itsrotational axis (15), the rotational axis (3,7,15) of the inner member(2), the center member (6) and the housing body (8) starting from acommon point.

The technical improvement that can be attained with the inventiveconfiguration of the joint resides particularly in its high rigidity andthe resulting high positioning precision.

The rolling bearings provided between the individual components of thejoint advantageously guarantee a comparatively low frictional resistanceand thus also a low pivoting resistance while, at the same time, atleast the pivoting ability of a conventional ball-and-socket joint isattained.

The center member has a disc-shaped configuration and is pivotallymounted with the help of two opposing angular needle bearings arrangedback-to-back. By angular needle bearings is meant that the effectivedirection of the force of pressure applied to each rolling element isinclined relative to the longitudinal axis of the pin. Due to theirradial compactness, the used needle bearings guarantee a particularlyspace-saving spatial arrangement.

The different configurations of the inner member which receives the pinare as follows. In one case, the inner member is disc-shaped and mountedwith the help of two opposing angular needle bearings arrangedface-to-face, or the inner member is spherical in shape and mounted withthe help of two angular needle bearings arranged back-to-back.

The housing body which receives the inner member and the center memberis mounted for rotation i the flange ring with the help of a crossroller bearing or by two opposing angular needle bearings arrangedface-to-face. Both types of mounting are equally feasible.

According to a further feature of the invention, the rolling bearingsare pre-stressed. This pre-stress prevents a radial displacement of thecomponents of the joint arranged in one another so that a particularlyhigh positioning precision can be achieved.

The housing body, the center member and the inner member are each madeof two pieces and joined together by fixing screws to form a unit. Thustwo-piece configuration assures the easy assembly of the rollingbearing-mounted joint.

Finally, the rolling bearing-mounted joint is used in machine tools ofthe hexapod system. These machine tools of a new generation are known tothe person skilled in the art and, in contrast to conventional machinetools, they move small masses. The result of this is that higheradjusting speeds are reached and, particularly, the rigidity between theframe and the tool holder is very high. Such a machine tool can comprisea plurality of arms which are articulated at one end on a frame and atthe other end, on a tool holder. The rolling bearing-mounted joints ofthe invention can be used advantageously in this type of machine tools.

The invention will now be described more closely with reference to thefollowing examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 4 and 5 are longitudinal sections through a rollingbearing-mounted joint, taken along the rotational axis of the housingbody,

FIGS. 2 and 3 are sections taken along lines II—II and III—IIIrespectively, of FIG. 1,

FIGS. 6 and 7 are sections taken along lines VI—VI and VII—VIIrespectively, of FIG. 5, and

FIG. 8 is a schematic representation of a machine tool of the hexapodsystem.

DETAILED DESCRIPTION OF THE DRAWINGS

The joint shown in FIGS. 1 to 3 in different sectional views comprises apin 1 which is received by an inner member 2. This inner member 2 isdisc-shaped and receives the pin 2 with an offset of 90° to itsrotational axis 3. The outer peripheral surface of the inner memberdrops obliquely outwards at its opposing axial ends so that two tracksextending at an acute angle to the rotational axis 3 are formed for twoangular needle bearings 4, 5. With the aid of these angular needlebearings 4, 5, the inner member 2 together with the pin 1 is arrangedfor pivoting in a center member 6. The inner member 2 is retained by thetwo angular needle bearings 4, 5 which are arranged face-to-face.

The center member 6 which receives the inner member 2 is again arrangedwith an offset of 90° to the rotational axis 3 of the inner member 2 forpivoting about its own axis 7 in a housing body 8. For this purpose, thecenter member 6 comprises on its outer peripheral surface, two trackswhich drop inwards at an acute angle to the rotational axis 7 forreceiving two angular needle bearings 9, 10 which are arrangedback-to-back and retain the center member 6. In direction towards thepin 1, the center member 6 comprises a recess 11 on its upper end whichenables a pivoting of the pin 1 within the center member 6.

The housing body 8 is arranged in a flange ring 12 with the help of twoangular needle bearings 13, 14 in face-to-face arrangement for rotationabout its rotational axis 15. The individual components, inner member 2,center member 6 and housing body 8, are inter-inserted in such a waythat their rotational axes 3, 7 and 15 intersect one another at a commonpoint, i.e. all three bearing center points are situated at the samepoint. It can be seen further from the three mentioned figures that thecenter member 6 and the housing body 8 are two-pieced and are joinedtogether by fixing screws 16, 17 to form a unit.

The difference between FIG. 1 and FIG. 4 is that the joint shown in thelatter is retained in the flange ring 12 with the help of a cross rollerbearing 18. Due to this threefold mounting of the joint on rollingbearings with the described advantages of rolling bearing-mounting, thepin 1, similar to a ball-and-socket joint, can take any position on anassociated spherical cap.

The joint shown in FIGS. 5 to 7 distinguishes itself by the fact thatthe inner member 2, which is made up of two parts connected to eachother by fixing screws 21, is spherical in shape and is mounted forpivoting about its rotational axis 3 by two angular needle bearings 19,20 arranged back-to-back.

The machine tool 28 shown in FIG. 8 comprises a plurality of telescopicarms 24 each of which is formed by inter-inserted tubes 22, 23. Thesetelescopic arms 24 are articulated at one end on a frame 25 and at theother end, on a tool holder 26. The tool holder 26 is provided with atool, not shown, which is driven by a motor 27. By retracting orextending one or more of the telescopic arms 24, the tool holder 26 canbe moved into any desired position in space. In the machine tool 28represented in FIG. 8, the inventive joints can be used advantageouslyboth on the frame 25 and on the tool holder 26.

What is claimed is:
 1. A joint having a pin (1) carrying an element thatis received via a rolling bearing for pivoting in an associated housing,wherein the pin (1) is received by an inner member (2), this innermember (2) is received via inner member four rolling bearings(4,5,19,20) arranged on its outer peripheral surface for pivoting aboutits rotational axis (3) in a center member (6), this center member (6)is received offset at 90° to the rotational axis (3) of the inner member(2) via center member rolling bearings (9,10) arranged on its outerperipheral surface for pivoting about its rotational axis (7) in ahousing body (8) which is mounted offset at 90° to the rotational axis(3) of the inner member (2) and to the rotational axis (7) of the centermember (6) in a flange ring (12) via housing body rolling bearings(13,14,18) arranged on its outer peripheral surface for rotation aboutits rotational axis (15), the rotational axes (3,7,15) of the innermember (2), the center member (6) and the housing body (8) starting froma common point.
 2. The joint according to claim 1 wherein the centermember (6) has a disc-shaped configuration and is pivotally mounted bytwo opposing center member angular needle bearings (9,10) arrangedback-to-back.
 3. The joint according to claim 1 wherein the inner member(2) is disc-shaped and is pivotally mounted by two opposing inner memberangular needle bearings (4,5) arranged face-to-face on its outerperipheral surface.
 4. The joint according to claim 1 wherein the innermember (2) is spherical in shape and is pivotally mounted by two innermember angular needle bearings (19,20) arranged back-to-back on itsouter peripheral surface.
 5. The joint according to claim 1 wherein thehousing body (8) is mounted for rotation in the flange ring (12) by ahousing body cross roller bearing (18) or by two housing body opposingangular needle bearings (13,14) arranged face-to-face.
 6. The jointaccording to claim 1 wherein all the rolling bearings(4,5,9,10,13,14,18,19,20) are pre-stressed.
 7. The joint according toclaim 1 wherein the housing body (8), the center member (6) and theinner member (2) are each made of two pieces and joined together byfixing screws (17,16,21,) to form a unit.
 8. The joint according toclaim 1 wherein it is used in machine tool (28) of hexapod system.